An image forming apparatus such as a copy machine sometimes includes, between the image forming apparatus and a finishing apparatus, a punching apparatus that applies punching to a sheet.
The punching apparatus displaces a punching mechanism according to a skew, i.e., a lateral shift of a sheet conveyed from the image forming apparatus. The displacement of the punching mechanism makes it possible to apply punching to appropriate places even in a skewed sheet.
A space for the displacement is necessary to displace the punching mechanism. If a curl occurs in a sheet, a leading end of the sheet enters the space to cause a bend of the sheet.
Therefore, there is a demand for a sheet processing apparatus and a sheet conveying method that less easily cause a bend of a sheet.